The present invention, in some embodiments thereof, relates to imaging devices and, more particularly, but not exclusively, to imaging system and methods for scientific and medical applications.
Endoscopic confocal microscopy devices are extensively used in minimally invasive medical diagnosis to look below tissue surfaces and for intervention purposes. Confocal microscopy is a technique generally used to acquire an image of a specimen and is based on focusing illuminating light from a point source to a point on the specimen, and focusing emitted light (responsive to the illuminating light) from the illuminated point on the specimen unto a small pinhole in an opaque screen. As only the emitted light from the illuminated point is focused unto the hole, the emitted light passes through the pinhole while all other light not emitted by the point is substantially blocked out. A detector on the other side of the screen detects the amount of emitted light passing through the pinhole and quantifies the amount for image reproduction purposes. As only one point in the specimen is illuminated at a time, two-dimensional (2D) or three-dimensional (3D) imaging generally is done by scanning over a regular raster (a rectangular pattern of parallel scanning lines) in the specimen.
A technique generally used to integrate confocal microscopy inside probes used in medical and scientific applications such as, for example, endoscopic probes and catheters, is spectrally encoded confocal microscopy (SECM). In SECM, the specimen is generally scanned line by line, with illuminating light at a different wavelength hitting each point along a line (each point on a line is “encoded” by a different wavelength). Emitted light from each point (each point emitting light at a different wavelength) is detected by a detector and, spatial information of the specimen along the line may be decoded by measuring the detected wavelengths. A 2D image may be reproduced by relatively slowly scanning the encoded lines mechanically within the probe.
An alternative technique to SECM is spectrally encoded endoscopy (SEE). SEE described in “Volumetric sub-surface imaging using spectrally encoded endoscopy”, by D. Yelin et al, Optics Express 1750/Vol. 16, No. 3/4 Feb. 2008; as follows: “Spectrally encoded endoscopy (SEE) [7] is a recently developed technique that utilizes wavelength to encode transverse image information. The SEE probe, comprising a single optical fiber, a diffraction grating, and a low NA lens, focuses spectrally dispersed light onto the sample. In turn, each point along this line is illuminated by a distinct spectral band. Each line of the image is acquired by measuring the spectrum of light reflected from the sample and returned back through the SEE probe using a high-speed spectrometer that resides outside the body. The second dimension of the image is obtained by moving the fiber at slow rates (e.g. 30 Hz). Without the need for rapid transverse scanning at the distal end of the endoscope, SEE allows video rate imaging to be performed through a miniature (i.e. 350 μm diameter) endoscopic device [13]. When the SEE probe is placed in the sample arm of an interferometer, it additionally can achieve three-dimensional topological, surface imaging in real-time, by use of time [14] and spectral [13, 15] domain low coherence interferometry.”
Use of SECM for spectrally encoded imaging of flowing blood cells is further described in “Flow cytometry using spectrally encoded confocal microscopy”, by D. Yelin and L. Golan, Optics, Volume 35, Issue 13, 2218-2220 (2010), which relates to “Flow cytometry techniques often rely on detecting fluorescence from single cells flowing through the cross section of a laser beam, providing invaluable information on vast numbers of cells. Such techniques, however, are often limited in their ability to resolve clusters of cells or parallel cell flow through large vessels. We present a confocal imaging technique that images unstained cells flowing in parallel through a wide channel, using spectrally encoded reflectance confocal microscopy that does not require mechanical scanning. Images of red blood cells from our system are compared to conventional transmission microscopy, and imaging of flowing red blood cells in vitro is experimentally demonstrated.”
It is known that green light is more susceptible to absorption by blood compared to the other colors in the light spectrum. This makes green light an important component for detecting blood vessels in the body. U.S. Publication No. 2008/0045817 to Van Beek et al describes, “Provided is a method and an apparatus for detection of objects below the surface of diffuse scattering media, in particular blood capillaries in organs such as the skin of human beings, using Orthogonal Polarized Spectral Imaging (OPSI), according to the invention comprising the steps of: imaging the object in question at least two different angles so as to obtain a shift of position in the imaging plane; and subsequently comparing relative shifts of objects in the two images so as to obtain coordinates of the imaged objects with respect to the organ surface.”